During our tests the capacity measured by the air enthalpy
method was typically 2 %e3 % lower than the capacity measured by
the refrigerant enthalpy. The main contribution for this difference is
conduction of heat through the enclosure walls. This effect was
significant because insulation was removed from the RTU's enclosure
in order to outfit it with the acrylic panels and provide visual
access inside during operation. The air infiltration into the negative
pressure compartment of the enclosure was another significant
factor to this difference. For this reason it was determined that the
refrigerant side capacity measurements would provide a better
basis for this work than the air-side capacity measurements, which
are required by the standard test method, since it is a direct measurement
of the evaporator's performance